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<div class="section predef_adding_new_predefs">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="predef.adding_new_predefs"></a><a class="link" href="adding_new_predefs.html" title="Adding new predefs">Adding new predefs</a>
</h2></div></div></div>
<p>
We know that a library like this one will be an eternal work-in-progress. And
as such we expect, and look forward to, others contributing corrections and
additions to the predefs. With that in mind we need to keep a consistent way
of defining the new predefs. Hence all current, and future, predefs follow
the same structure and requirements.
</p>
<h4>
<a name="predef.adding_new_predefs.h0"></a>
<span><a name="predef.adding_new_predefs.requirements_of_the_header"></a></span><a class="link" href="adding_new_predefs.html#predef.adding_new_predefs.requirements_of_the_header">Requirements
of the header</a>
</h4>
<p>
All predefs need to follow a set of requirements:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
The headers must use the Boost Software License.
</li>
<li class="listitem">
The predef must, by default, be defined as <code class="computeroutput"><span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="number">0</span><span class="special">,</span><span class="number">0</span><span class="special">,</span><span class="number">0</span><span class="special">)</span></code>.
</li>
<li class="listitem">
The predef must be redefined to a non-zero value once detected.
</li>
<li class="listitem">
The predef must, by default, be defined to <code class="computeroutput"><span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="number">0</span><span class="special">,</span><span class="number">0</span><span class="special">,</span><span class="number">1</span><span class="special">)</span></code> when the predef is detected.
</li>
<li class="listitem">
If possible, the predef will be defined as the version number detected.
</li>
<li class="listitem">
The predef must declare itself, after being defined, for the testing system.
</li>
</ul></div>
<p>
And there are some extra guidelines that predef headers should follow:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
The detection should avoid including extra headers that might otherwise
not be included by default.
</li>
<li class="listitem">
If the detection must include a header, prefer guarding it within the detection
if possible.
</li>
<li class="listitem">
If the detection must include headers unconditionally, and has a choice
of headers to include, prefer the ones with the least impact. I.e. include
the one with the minimal set of definitions and other dependencies.
</li>
</ul></div>
<h4>
<a name="predef.adding_new_predefs.h1"></a>
<span><a name="predef.adding_new_predefs.structure_of_the_header"></a></span><a class="link" href="adding_new_predefs.html#predef.adding_new_predefs.structure_of_the_header">Structure
of the header</a>
</h4>
<p>
For general consistency it's suggested that new predef headers follow the structure
below, as current predef headers do. First we have the copyright and license
statement, followed by the include guard:
</p>
<pre class="programlisting"><span class="comment">/*
Copyright Jane Doe YYYY
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE_1_0.txt or copy at
http://www.boost.org/LICENSE_1_0.txt)
*/</span>
<span class="preprocessor">#ifndef</span> <span class="identifier">BOOST_PREDEF_category_tag_H</span>
<span class="preprocessor">#define</span> <span class="identifier">BOOST_PREDEF_category_tag_H</span>
</pre>
<p>
Depending on how you are defining the predef you will at minimum have to include
the <code class="computeroutput"><span class="identifier">version_number</span><span class="special">.</span><span class="identifier">h</span></code> header. But you might also want to include
the <code class="computeroutput"><span class="identifier">make</span><span class="special">.</span><span class="identifier">h</span></code> header for the version number decomposing
utility macros:
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">predef</span><span class="special">/</span><span class="identifier">version_number</span><span class="special">.</span><span class="identifier">h</span><span class="special">&gt;</span>
<span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">predef</span><span class="special">/</span><span class="identifier">make</span><span class="special">.</span><span class="identifier">h</span><span class="special">&gt;</span>
</pre>
<p>
The Predef library uses Quickbook for documentation and for the individual
predefs to appear in the reference section we add in-code documentation followed
by the zero-value default definition of the predef macro. We strongly recommend
this particular placement of the documentation and default definition because
some development environments automatically interpret this and provide in-line
help for the macro. In particular this works for the popular Eclipse IDE:
</p>
<pre class="programlisting"><span class="comment">/*`
[heading `BOOST_category_tag`]
Documentation about what is detected.
*/</span>
<span class="preprocessor">#define</span> <span class="identifier">BOOST_category_tag</span> <span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="number">0</span><span class="special">,</span><span class="number">0</span><span class="special">,</span><span class="number">0</span><span class="special">)</span>
</pre>
<p>
Next is the detection and definition of the particular predef. The structure
for this is to do a single overall check (<code class="computeroutput"><span class="identifier">condition_a</span></code>)
and place further version detection inside this. The first action inside the
overall check is to "<code class="computeroutput"><span class="preprocessor">#undef</span>
<span class="identifier">BOOST_category_tag</span></code>" which undefines
the zero-value default. The rest is up to the you how to do the checks for
defining the version. But at minimum it must "<code class="computeroutput"><span class="preprocessor">#define</span>
<span class="identifier">BOOST_category_tag</span> <span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="number">0</span><span class="special">,</span><span class="number">0</span><span class="special">,</span><span class="number">1</span><span class="special">)</span></code>" as the fallback to minimally indicate
that the predef was detected:
</p>
<pre class="programlisting"><span class="preprocessor">#if</span> <span class="special">(</span><span class="identifier">condition_a</span><span class="special">)</span>
<span class="preprocessor">#undef</span> <span class="identifier">BOOST_category_tag</span>
<span class="preprocessor">#if</span> <span class="special">(</span><span class="identifier">condition_b</span><span class="special">)</span>
<span class="preprocessor">#define</span> <span class="identifier">BOOST_category_tag</span> <span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="identifier">major</span><span class="special">,</span><span class="identifier">minor</span><span class="special">,</span><span class="identifier">patch</span><span class="special">)</span>
<span class="preprocessor">#else</span>
<span class="preprocessor">#define</span> <span class="identifier">BOOST_category_tag</span> <span class="identifier">BOOST_VERSION_NUMBER</span><span class="special">(</span><span class="number">0</span><span class="special">,</span><span class="number">0</span><span class="special">,</span><span class="number">1</span><span class="special">)</span>
<span class="preprocessor">#endif</span>
<span class="preprocessor">#endif</span>
</pre>
<p>
The testing of the predef macros is automated to generate checks for all the
defined predefs, whether detected or not. To do this we need to declare the
predef to the test system. This declaration is empty for regular use. And during
the test programs they expand out specially to create informational output:
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">predef</span><span class="special">/</span><span class="identifier">detail</span><span class="special">/</span><span class="identifier">test</span><span class="special">.</span><span class="identifier">h</span><span class="special">&gt;</span>
<span class="identifier">BOOST_PREDEF_DECLARE_TEST</span><span class="special">(</span><span class="identifier">BOOST_category_tag</span><span class="special">,</span><span class="string">"Name"</span><span class="special">)</span>
</pre>
<p>
And, of course, we last need to close out the include guard:
</p>
<pre class="programlisting"><span class="preprocessor">#endif</span>
</pre>
<h4>
<a name="predef.adding_new_predefs.h2"></a>
<span><a name="predef.adding_new_predefs.using_utility_pattern_macros"></a></span><a class="link" href="adding_new_predefs.html#predef.adding_new_predefs.using_utility_pattern_macros">Using utility
pattern macros</a>
</h4>
<p>
By including:
</p>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">predef</span><span class="special">/</span><span class="identifier">make</span><span class="special">.</span><span class="identifier">h</span><span class="special">&gt;</span>
</pre>
<p>
One will get a set of utlity macros to decompose common version macros as defined
by compilers. For example the EDG compiler uses a simple 3-digit version macro
(M,N,P). It can be decomesed and defined as:
</p>
<pre class="programlisting"><span class="preprocessor">#define</span> <span class="identifier">BOOST_CXX_EDG</span> <span class="identifier">BOOST_PREDEF_MAKE_N_N_N</span><span class="special">(</span><span class="identifier">__EDG_VERSION__</span><span class="special">)</span>
</pre>
<p>
The decomposition macros are split into three types: decimal decomposition,
hexadecimal decomposition, and date decomposition. They follow the format of
using "N" for decimal, "F" for hexadecimal, and "Y",
"M", "D" for dates.
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright &#169; 2005 Rene Rivera<br>Copyright &#169; 2008-2011 Redshift
Software Inc<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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